Plate-type reactor with in-situ injection

ABSTRACT

A chemical reactor including: a plurality of heat exchange plates which between them define reaction compartments, in which reactor each heat exchange plate includes two walls between them defining at least one heat exchange space, the respective walls being fixed together by joining regions, and the reactor also comprises at least one injection device for injecting substance into the reaction compartments, said substance-injection device passing through the heat-exchange plates in respective joining regions thereof. Also, a chemical reaction process that can be carried out in this reactor.

The present invention relates to a chemical reactor exhibiting ageometry of plate type which makes possible the in situ injection of asubstance, such as oxygen, into the reaction medium, optionally inmultistaged fashion. The invention also relates to a chemical reactionprocess using said reactor.

TECHNICAL BACKGROUND

The use of chemical reactions, in particular involving heterogeneouscatalysis, in fixed bed reactors is known. When these chemical reactionsare highly endothermic or highly exothermic, control of the heatabsorbed or emitted by the reaction presupposes that the reactor hasavailable extensive heat-exchange surfaces.

For example, a conventional geometry of fixed bed chemical reactors isthe multitubular geometry. This geometry exhibits in particular thedisadvantage of involving relatively complex and lengthy operations forcharging and discharging catalyst which result in losses inproductivity. Furthermore, multitubular reactors exhibit a very highmanufacturing cost but also a very high weight related to the masses ofmetals which it is necessary to use. Another constraint on thesereactors is related to their method of manufacture and transportation:they are limited in size as, manufactured and tested in a factory, theysubsequently have to be transported to the site of final use.

Another geometry known for these reactors is the plate geometry. In aplate reactor, the reaction compartments are delimited by heat-exchangeplates. The documents EP 0995491 and EP 1147807 provide examples of suchplate reactors.

Another example appears in the document US 2005/0020851, which describessuch a reactor used for the oxidation of a C₃ or C₄ precursor to giveacrolein, methacrolein, acrylic acid or methacrylic acid.

The document US 2005/0158217 also describes a reactor of this type, inwhich thermocouples are positioned in the reaction compartments (withoutpassing through them) in order to control the reaction.

The document US 2005/0226793 describes a specific arrangement ofheat-exchange plates, in which arrangement the projections of each plateare facing the reinforcements of the adjacent plate and vice versa, inorder to improve the control of the temperature.

Finally, the document US 2006/0276334 provides another example of areactor of this type, in which the heat-exchange plates comprise acracked coating (deposit).

All the above reactors exhibit the disadvantage of not making possiblesufficient control/management of the temperature in the reactor, in thereaction phase and/or in the regeneration phase.

There thus exists a real need to make possible better control of thetemperature in fixed bed reactors.

SUMMARY OF THE INVENTION

The invention relates first to a chemical reactor comprising a pluralityof heat-exchange plates defining, between them, reaction compartments,in which reactor each heat-exchange plate comprises two walls defining,between them, at least one heat-exchange space, the respective wallsbeing fixed to one another by joining regions, and the reactor alsocomprises at least one device for injection of substance into thereaction compartments, said substance-injecting device passing throughthe heat-exchange plates in respective joining regions of the plates.

According to one embodiment, the substance-injecting device is a devicefor the injection of gas and preferably a device for the injection ofoxygen-comprising gas.

According to one embodiment, the substance-injecting device is a pipeexhibiting a plurality of injection orifices.

According to one embodiment, the joining regions are positioned on theheat-exchange plates in the form of strips, preferably parallel strips,or in the form of points.

According to one embodiment, the chemical reactor comprises a pluralityof substance-injecting devices, preferably parallel to one another andpreferably connected to a substance-distributing system.

According to one embodiment, the heat-exchange plates are positioned ina chamber in a radial manner or in a manner parallel to one another andare preferably grouped into modules.

The invention also relates to a chemical reaction process comprising theadmission of reactants at the inlet of a reaction compartment definedbetween two heat-exchange plates, the withdrawal of reaction products atthe outlet of the reaction compartment, and the injection of a substanceinto the reaction compartment, in which process each heat-exchange platecomprises two walls defining, between them, at least one heat-exchangespace, the respective walls being fixed to one another by joiningregions, and the injection of substance being carried out by means of atleast one substance-injecting device which passes through theheat-exchange plates in respective joining regions of the plates.

According to one embodiment, the reaction is of the heterogeneouscatalytic type and a catalyst is positioned in the reactioncompartments, preferably in the form of solid particles.

According to one embodiment, the process alternately comprises phases ofproduction and phases of regeneration of the catalyst, the injection ofsubstance being carried out during the reaction phases and/or during theregeneration phases.

According to one embodiment, the substance is a reactant or a catalyticcompound or a compound capable of regenerating a catalyst.

According to one embodiment, the substance is an oxygen-comprising gas.

According to one embodiment, the substance is injected at several pointsof the route of the reactants in the reaction compartment.

According to one embodiment, the process is carried out in a chemicalreactor as described above.

According to one embodiment, the process is:

-   -   a process for the dehydration of glycerol to give acrolein; or    -   a process for the dehydration of lactic acid to give acrylic        acid; or    -   a process for the dehydration of 3-hydroxypropionic acid to give        acrylic acid; or    -   a process for the dehydration of 3-hydroxyisobutyric acid to        give methacrylic acid; or    -   a process for the dehydration of 2-hydroxyisobutyric acid, also        known as alpha-hydroxyisobutyric acid, to give methacrylic acid;        or    -   a process for the preparation of a hydrofluoroolefin or of a        hydrofluorocarbon, preferably a process for the preparation of a        fluoropropene and very particularly preferably a process for the        preparation of 2,3,3,3-tetrafluoropropene.

The present invention makes it possible to overcome the disadvantages ofthe state of the art. It more particularly provides a fixed bed reactorin which the control of the temperature at any point of the reactor isimproved.

This is accomplished by virtue of a plate reactor geometry, in which aninjection of a substance in situ into the reaction compartments iscarried out by means of injection devices which pass through the plates.This injection makes it possible to exert better control over thechemical processes in the combined reaction compartments by modifyingthe composition of the reaction stream or the reaction conditions insitu.

According to certain specific embodiments, the invention also exhibitsone or preferably several of the advantageous characteristics listedbelow.

-   -   The invention is particularly appropriate for the implementation        of reactions in which the catalyst is susceptible to        deactivation by coking and has to be regenerated by combustion.        This is because, by choosing an oxygen-comprising gas as        substance injected in situ, it is possible to carry out the        regeneration much more rapidly, with a better homogeneity in        temperature in the reactor. Furthermore, the risks of explosion        or runaway are limited by avoiding a high oxygen partial        pressure at the inlet of the reactor.    -   The invention makes it possible to achieve an increase in yield        of the order of several percent. The invention also makes it        possible to limit the down times of the reactor for regeneration        and thus to obtain an increase in productivity typically of the        order of 25% to 100%.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents, in perspective and in exploded view, a portion of areactor according to one embodiment of the invention.

FIGS. 2 and 3 represent, in perspective and in section, details of aheat-exchange plate in a reactor according to one embodiment of theinvention.

FIG. 4 represents a section of a portion of a reactor according to oneembodiment of the invention.

FIG. 5 represents, in perspective and in section, details of aheat-exchange plate in a reactor according to another embodiment of theinvention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in more detail and without limitation inthe description which follows.

General Description of the Reactor

With reference mainly to FIGS. 1 and 4, generally, the reactor accordingto the invention comprises a chamber, which is advantageouslyessentially cylindrical with a circular section, inside which ispositioned an assembly of heat-exchange plates 1 delimiting, betweenthem, reaction compartments 3.

The reaction compartments 3 are advantageously filled with a catalystappropriate for the reaction carried out, this catalyst preferably beingin the form of solid particles (beads, grains or powder) or in the formof porous monolith or of blocks of porous monolith.

The reactor can operate according to at least two modes, namely aproduction mode, during which the targeted chemical reaction takes placein the reaction compartments; and a regeneration mode, during which theat least partially deactivated catalyst is regenerated.

In the context of the present patent application, the expression“reaction stream” is understood within the broad sense and denotes astream passing through the reaction compartments 3, it being understoodthat the composition of the reaction stream varies between the inlet andthe outlet of the reaction compartments 3.

In the production phase, the reaction stream at the inlet of thereaction compartments 3 comprises all or part of the reactants (it beingpossible for another part of the reactants optionally to be introducedvia the substance-injecting devices described below) and the reactionstream at the outlet of the reaction compartments 3 comprises, at leastin part, the products of the reaction.

In the regeneration phase, the reaction stream at the inlet of thereaction compartments 3 can comprise one or more compounds capable ofregenerating the catalyst, and the reaction stream at the outlet of thereaction compartments 3 comprises residues from the regeneration.Alternatively, the reaction stream at the inlet of the reactioncompartments 3 can be a simple inert stream (it being possible for thecompounds capable of regenerating the catalyst to be injected by meansof the substance-injecting devices 6 described below).

In comparison with a multitubular geometry, a plate geometry exhibits agreater simplicity of manufacture, of use and of maintenance.

Each heat-exchange plate 1 defines a mean plane. The term “length”denotes the dimension of the plates 1 in this plane along the main axisof the chamber of the reactor (cylindrical axis in general) and the term“width” denotes the dimension of the plates 1 orthogonal to thepreceding dimension in this same plane.

Generally, the axis of the chamber of the reactor is positioned alongthe vertical direction. This implies that the length of the plates 1 isalong the vertical direction and that the width and the thickness of theplates 1 are along horizontal directions.

The width of the plates 1 is generally dictated by manufacturingconsiderations; it can, for example, be from 100 to 2500 mm and inparticular from 500 to 1500 mm. The length of the plates 1 depends onthe reaction and in particular on its temperature profile. It can, forexample, be from 500 to 7000 mm and in particular from 3000 to 4000 mm.

According to one embodiment, the heat-exchange plates 1 are positionedaccording to a radial arrangement in the chamber. Such a radialarrangement is described, for example, in the document US 2005/0226793,in connection in particular with FIG. 6. This arrangement makes possibleoptimum use of all of the chamber of the reactor, when the chamber iscylindrical with a circular cross section

According to an alternative embodiment to the above, and which ispreferred in order to simplify and render uniform the flow of thereaction stream, the heat-exchange plates 1 are positioned essentiallyparallel to one another, so that the reaction compartments 3 are volumeswith an overall uniform thickness (apart from the local deformation ofthe heat-exchange plates 1).

In this case, in order to make possible better use of the spaceavailable in the chamber, it can be advantageous to divide up theheat-exchange plates 1 and the interposed reaction compartments 3 intoreaction modules of rectangular parallelepipedal form. Such anarrangement of the heat-exchange plates 1 into modules is described, forexample, in the document US 2005/0020851, in particular in connectionwith FIGS. 1A, 1C, 1D, 1E and 1F.

Such a modular structure can make it possible to adapt the reactor in aflexible manner with regard to the capacity required, for example byinstalling only a portion of the modules in the reactor, in order toadjust the capacity thereof, or by closing some modules in order toisolate them from the reaction stream.

The modules can have the same dimensions, which simplifies themanufacture thereof. They can also have different dimensions, in orderto optimize the occupation of the space in the chamber of the reactor.

Preferably, the modules can be individually withdrawn, replaced orexchanged, which simplifies the maintenance operations.

Each module is preferably held in position and stabilized in the chamberby an appropriate guide, for example a rectangular frame 10, to whichthe plates 1 of the module can be fixed by fixing means 11. The guidesor frames 10 of the various modules can be sealed from one another toprevent any flow from one module to the other.

The intermediate space located between the wall of the chamber and theadjacent module or modules can be separated from the reactioncompartments 3 by sealing (and optionally by filling with inertmaterials and by pressurization), in order to prevent any reaction oraccumulation of material in this region.

Various possible forms of installing the modules in the chamber and ofsealing the assembly are described in detail in the document US2005/0020851.

With reference mainly to FIGS. 2 to 5, each heat-exchange plate 1 isformed of two walls 2 a, 2 b, between which at least one heat-exchangespace 4 is arranged. The walls 2 a, 2 b can, for example, consist ofsheets of stainless steel, generally of rectangular shape. The thicknessof the walls 2 a, 2 b can, for example, be from 1 to 4 mm, in particularfrom 1.5 to 3 mm and especially from 2 to 2.5 mm.

The two walls 2 a, 2 b are fixed to one other by joining regions 5. Thisfixing can be carried out, for example, by welding the walls 2 a, 2 b toone another. The joining regions 5 can be of any shape.

According to one embodiment, the joining regions 5 are in the form ofpoints (as is the case in FIGS. 1 to 4).

The term “points” is understood here to mean joining regions 5exhibiting a relatively small size with respect to the total size of theheat-exchange plate 1, this being the case both in the direction of thelength and in the direction of the width of the heat-exchange plate 1.

By way of example, each joining region 5 of point type exhibits a widthof less than or equal to 5% or of less than or equal to 1% or of lessthan or equal to 0.5% of the total width of the plate, and also a lengthof less than or equal to 5% or of less than or equal to 1% or of lessthan or equal to 0.5% of the total length of the plate 1.

Thus, the “point-form” joining regions 5 can preferably have acircular/discal shape but also optionally a polygonal shape (forexample, shape of squares).

When the joining regions 5 are in the form of “points” within themeaning of the present patent application, these points can bedistributed according to a two-dimensional network over eachheat-exchange plate 1, for example a network having a rectangular meshor having a square mesh; or according to a hexagonal paving, forexample.

According to a specific embodiment, the joining regions 5 in the form ofpoints are distributed in parallel lines, the spacing between thesuccessive joining regions within one and the same line being, forexample, from 30 to 80 mm, or from 35 to 70 mm, or from 40 to 60 mm. Inaddition, the lines of points are preferably equidistant, with aseparation between lines, for example, of 5 to 80 mm, or of 8 to 70 mm,or of 10 to 60 mm. The successive lines of points can be offset withrespect to one another along the direction of the lines, for example byhalf a spacing between points of one and the same line. In other words,in this case, the points of the lines are in orthogonal alignment to thelines in a proportion of one line out of two.

According to another embodiment represented in FIG. 5, the joiningregions 5 are in the form of strips, that is to say of lines. The stripscan be curved or, preferably, straight. The (successive) adjacent stripsare preferably parallel to one another and, for example, equidistant.These strips can, for example, be positioned in the direction of thelength of the heat-exchange plates 1 or along their width. By way ofexample, the distance between strips can be from 100 to 1500 mm andpreferably from 400 to 1000 mm, when they are arranged in the directionof the length of the reactor, and from 5 to 2000 mm and preferably from40 to 120 mm, when they are arranged in the direction of the width ofthe reactor.

When the joining regions 5 are in the form of points, the heat-exchangespace 4 between the walls 2 a, 2 b of the heat-exchange plate 1 isgenerally a single space. On the other hand, when the joining regions 5are in the form of strips, the heat-exchange space 4 between the walls 2a, 2 b of the heat-exchange plate 1 is generally composed of a pluralityof channels delimited by successive joining regions 5.

It should be noted that it is possible to combine joining regions 5 inthe form of points with joining regions 5 in the form of strips. Inaddition to the joining regions 5 described above, the walls 2 a, 2 b ofeach heat-exchange plate 1 are advantageously joined to one another orsealed at their periphery in order to confine the heat-exchange fluid inthe heat-exchange space 4. Preferably, this joining or this sealing isnot complete, in order to insert at least one opening for the entry ofthe heat-exchange fluid into the heat-exchange space 4 and at least oneopening for the departure of the heat-exchange fluid.

Generally, a heat-exchange fluid is circulated in the heat-exchangespace 4 of each plate 1 in order to introduce heat into the reactioncompartments 3 (case of an endothermic reaction) or in order to removeheat from the reaction compartments (case of an exothermic reaction).The heat-exchange fluid can also be a mineral oil or a synthetic oil,for example a Jarytherm or a Dowtherm. The heat-exchange fluid can alsobe a mixture of molten nitrates and/or nitrites, for example a eutecticmixture of sodium nitrate, potassium nitrate and sodium nitrite, havinga low melting point and a high heat capacity. Preferably, theheat-exchange fluid is used for purposes of removal of heat.

The heat-exchange fluid can in particular be an aqueous solutionoptionally comprising additives, such as hydrazine or ammonia or acorrosion inhibitor. The circulation of the heat-exchange fluid in theheat-exchange spaces 4 can be of cocurrent or countercurrent ortransverse (crossed) type, with respect to the circulation of thereaction stream in the adjacent reaction compartments 3.

For optimum heat transfer, the heat-exchange fluid partially changes instate during its passage through the heat-exchange space 4; for example,it changes at least partially from the liquid state to the vapor statein the case of an exothermic reaction.

In order to make possible the presence of the heat-exchange fluid in theheat-exchange spaces 4, the walls 2 a, 2 b of the heat-exchange plates 1are deformed (swollen) at a distance from the joining regions 5. Inother words, each heat-exchange plate 1, in use, comprises portions ofminimum thickness (or depressions) at the joining regions 5 of the walls2 a, 2 b, and portions of maximum thickness (or protuberances 12) at adistance from the joining regions 5 of the walls 2 a, 2 b.

It is possible to position the joining regions 5 on the plates 1 and toalign the successive heat-exchange plates 1 so that the protuberances 12of the respective plates 1 are aligned and that the depressions of therespective plates 1 are aligned orthogonally to the plates. Such anarrangement facilitates the installation of the substance-injectingdevices 6 described below, perpendicularly to the plates 1.

However, it is also possible to position the joining regions 5 on theplates 1 and to align the successive heat-exchange plates 1 so that theprotuberances 12 of the respective plates 1 are offset and that thedepressions of the respective plates 1 are offset. For example, theprotuberances 12 of each plate 1 can be aligned with the depressions ofits neighboring plate or plates 1 orthogonally to the plates 1 and viceversa. Such an arrangement makes it possible to reduce the variations inthickness of the reaction compartments 3. The document US 2005/0226793provides an example of an arrangement of this type. In the context ofthe invention, this arrangement requires, however, that thesubstance-injecting devices 6 described below be positioned in aninclined manner with respect to the direction orthogonal to the plates1, which can complicate the design of the reactor.

Typically, the minimum thickness of the reaction compartments 3 (that isto say, the thickness at the point or at the points where the adjacentplates are the least spaced out) is from 8 to 150 mm, for example from10 to 100 mm, in particular from 12 to 50 mm, especially from 14 to 25mm and, by way of illustration, from 16 to 20 mm. In any case, thethickness of the reaction compartments 3 has to be adapted in order tobe able to fill the reaction compartments 3 with the catalyst, which is,for example, in the form of grains. The catalyst grains generally have asize (Dv50) of 1 to 10 mm, for example of approximately 5 mm. It isdesirable for the thickness of the reaction compartments 3 to be of theorder of 3 to 5 grains at least, in order to be able to easily fillthem. Use may also be made of the catalyst forms as monolithic blockswith a thickness of 20 mm, for example.

It is also possible to provide reaction compartments 3 with differentthicknesses within the reactor.

The reaction compartments 3 can be isolated from one another by sealingor else they can be in communication via their ends.

Spacing elements can be provided between the successive heat-exchangeplates 1, in order to limit the deformations of the plates 1 and therelative displacements of the plates 1.

A system for distributing heat-exchange fluid and a system forcollecting heat-exchange fluid are provided on either side of theheat-exchange plates 1. It is possible, for example, to provide amodular distribution system and a modular collecting system.

The heat-exchange fluid can circulate naturally or in forced fashion inthe heat-exchange spaces 4. In this second case, pumping means can beprovided at the inlet.

Thermal expansion joints can be provided on the chamber (at theperiphery and/or at the ends of the latter). The abovementioneddistribution systems advantageously exhibit curved or angular portionswhich make it possible to compensate for the thermal expansion.

A system for distribution of reaction stream 9 and a system forcollecting reaction stream (not represented) are provided on either sideof the reaction compartments 3. It is possible, for example, to providea modular distribution system and a modular collecting system. Thereaction stream can be of liquid or gaseous or mixed type. The reactionstream can circulate from the top downward or from the bottom upwardwith respect to the chamber.

Catalyst-retaining means (typically perforated plates) are provided atthe inlet and at the outlet of the reaction compartments 3.

It is possible to provide baffling in the reaction compartments 3 and/orin the heat-exchange space 4, in order to force the heat-exchange fluidand/or the reaction stream to flow along a predetermined route.

Injection of Substance in Situ into the Reaction Compartments

The invention provides at least one substance-injecting device 6 in thereaction compartments 3, preferably a plurality. The substance-injectingdevices 6 pass through the heat-exchange plates 1 and the reactioncompartments 3 between the heat-exchange plates 1.

According to the embodiment illustrated in the figures, which isparticularly simple to implement, the substance-injecting devices 6 aresubstance-injecting pipes 6, essentially parallel to one another andpreferably orthogonal to the heat-exchange plates 1.

The substance-injecting pipes 6 can, for example, be manufactured fromstainless steel or from porous ceramic.

The substance-injecting pipes 6 pass through the heat-exchange plates 1at the joining regions 5 described above. Thus, any risk ofcommunication between the heat-exchange spaces 4 occupied by theheat-exchange fluid and the reaction compartments 3 occupied by thereaction stream is avoided.

To do this, the joining regions 5 have to exhibit dimensions which aresufficient to allow an opening 7 to be drilled within these joiningregions 5 without compromising the leaktightness of the heat-exchangespace 4, the opening 7 being appropriate for the passage of thesubstance-injecting pipe 6.

The substance-injecting pipes 6 have, for example, a diameter of 10 to100 mm and preferably of 20 to 50 mm (in order for them to havesufficient stiffness to allow assembling). The joining regions 5, whichconsist, for example, of welds of circular shape, preferably exhibit, attheir center, respective openings 7 with a diameter slightly greater(for example from 1 to 5 mm) than that of the substance-injecting pipes6.

Sealing means can be provided around the substance-injecting pipes 6 atthe openings 7 on the joining regions 5 if it is desired to prevent anycommunication between reaction compartments 3.

Furthermore, each substance-injecting pipe 6 comprisessubstance-injecting means, which can be simple orifices, preferably overthe whole of its length passing through the reaction compartments 3.

All of the substance-injecting pipes 6 can be connected to at least onesubstance-distributing system 8 (itself connected to a supply ofsubstance to be injected). It is possible to providesubstance-distributing systems which are independent between the modulesor a single substance-distributing system for all of the modules.Optionally, at least one substance-collecting system (not represented)or several, for example one per module, is/are also provided at theopposite end of the substance-injecting pipes 6 with respect to thesubstance-distributing system(s) 8. This proves to be useful when it isdesirable for only a portion of the substance stream circulating in thepipe 6 to pass into the reaction compartments 3 which have been passedthrough (for example in order to guarantee a sufficient pressure at anyinjection point).

When the joining regions 5 are in the form of points, it is possible toprovide a substance-injecting device 6 which passes through each joiningregion 5, or else it is possible to provide substance-injecting devices6 which pass through only some joining regions 5, the other joiningregions 5 then preferably being devoid of opening 7: it is thisembodiment which is represented in FIGS. 1 to 4.

When the joining regions 5 are in the form of strips, it is possible toprovide a substance-injecting device 6 which passes through each strip,or else it is possible to provide substance-injecting devices 6 whichpass through only some strips, the other strips then preferably beingdevoid of opening 7. It is also possible to provide severalsubstance-injecting devices 6 which pass through one and the same strip,the latter being drilled with a number of openings appropriate for thenumber of substance-injecting devices 6 passing through it.

Preferably, the arrangement of the substance-injecting devices 6 makespossible an essentially homogenous injection of the substance into thereaction compartments 3.

The substance injected into the reaction compartments 3 by means of thesubstance-injecting devices can be a gas or a liquid or a mixture of thetwo.

It can be a reactant or a catalytic compound or a compound capable ofregenerating the catalyst present in the reaction compartments 3.

It is possible to inject substance into the reaction compartments 3solely during the production phase or solely during the regenerationphase or during both phases.

It is also possible to inject different substances over time (forexample, a first substance when the reactor operates in the productionphase and a second substance when the reactor operates in theregeneration phase).

Preferably, the substance injected is an oxygen-comprising gas, forexample virtually pure oxygen, or air, or a mixture of inert gas andoxygen.

This is because, for the reactions in which the catalyst is deactivatedby coking, the injection of oxygen during the regeneration phase makesit possible to carry out combustion and thus regeneration of thecatalyst, this being carried out with better control of the temperaturein all the reaction compartments and with greater safety. In particular,it is thus possible to avoid displacement of hot front through theentire catalyst bed. In addition, the injection of oxygen during theproduction phase can make it possible to extend the duration ofdeactivation of the catalyst, still with the abovementioned benefits interms of improved control of the temperature and safety.

The injection of oxygen is also of use for the catalysts, theregeneration of which involves an oxygenation, such as, for example,catalysts of bismuth molybdate type used for the oxidation of propyleneto give acrolein and of isobutene/t-butanol to give methacrolein, orcatalysts of iron molybdate type used for multiple reactions, such asthe oxidation of methanol to give formaldehyde, the oxidation of ethanolto give acetaldehyde, the oxidation of methanol to givedimethoxymethane, the oxidation of ethanol to give diethoxyethane, andthe like.

Another example of substance injected is chlorine, in particular in thecontext of the implementation of fluorination reactions. This is becausethe injection of chlorine in the production phase makes it possible toinhibit reactions in which the catalyst is deactivated.

If required, the stream of the injected substance can be adjusteddifferently according to the injection sites. Pumping or compressingmeans and valves make it possible to regulate the flow rate of substancein each substance-injecting device 6 and in each reaction compartment 3.

Reactions which can be Carried out According to the Invention

The invention is advantageously employed for the production of acrylicacid of renewable origin, in particular the production of acrylic acidfrom glycerol, comprising a first stage of dehydration of the glycerolto give acrolein, followed by a stage of oxidation in the gas phase ofthe acrolein thus obtained; or in the production of acrylic acid bydehydration of 2-hydroxypropionic acid (lactic acid) or3-hydroxypropionic acid and their esters.

The invention makes it possible in particular to carry out a process forthe dehydration of glycerol to give acrolein. In this type of process,the glycerol is fed in the form of an aqueous solution with aconcentration of 20 to 95% by weight. The more concentrated theglycerol, the greater the tendency of the catalysts to form coke, whichnecessitates regularly regenerating the catalyst. According to theprocess described in the application WO 2006/087083, the reaction isadvantageously carried out in the presence of oxygen, the addition ofoxygen to the reaction for the dehydration of glycerol making itpossible to extend the lifetime of the catalyst and to space out theregenerations.

The reaction is typically carried out at a temperature of 220 to 350° C.and preferably of 280 to 320° C. , and at a pressure varying fromatmospheric pressure to a few bar (for example 5). The concentration ofthe reactants is in part dictated or imposed by the flammability limits.In the reactors of the prior art, the flammability limits of an O₂/inertgas/glycerol/steam gas mixture prescribe a low concentration of glyceroland oxygen in the gas phase.

With the reactor of the invention, it is possible to employ a mixturewhich is richer in glycerol than with the reactors of the prior art, asadditional oxygen is introduced by injection in situ. For example, it ispossible to use mixtures comprising 6% of glycerol and from 1 to 2% ofoxygen, the remainder being introduced in situ.

The catalysts which can be used for this reaction are acid catalysts, inparticular having a Hammett acidity of less than +2, such as described,for example, in the documents EP 1 848 681, WO 2009/12855, WO2009/044081 or WO 2010/046227. Many acid catalysts may be suitable forthis reaction. Mention will be made of phosphated zirconias, tungstatedzirconias, silica zirconias, titanium or tin oxides impregnated withtungstate or phosphotungstate or silicotungstate, phosphated aluminas orsilicas, heteropolyacids or heteropolyacid salts, iron phosphates andiron phosphates comprising a promoter.

In the context of this process, the catalyst undergoes deactivation, inparticular by coking. However, this deactivation can be delayed by theinjection of oxygen in situ into the reaction compartments of thereactor, in the production phase. The O₂/glycerol molar ratio at thereactor inlet is from 0.1 to 1.5 (preferably from 0.3 to 1.0) and theoxygen partial pressure is less than 7%. The addition of supplementaryoxygen, in the form of molecular oxygen, of air or of a mixture ofoxygen and a gas which is inert for the reaction, is distributed overthe length of the reactor. Preferably, between 2 and 10 injection sitesare provided over the length of the reactor. The cumulative partialpressure of the oxygen added along the reactor is thus from 1 to 10%.

Furthermore, in the regeneration phase, the injection of oxygen in situinto the reaction compartments of the reactor makes it possible toregenerate the catalyst in a safe and controlled manner.

Generally, in the regeneration phase, it is necessary to properlycontrol the temperature of the catalyst in order to prevent conditionsfor runaway of the reaction, resulting in very high rises in thetemperature of the catalyst which can irreversibly damage it and evendamage the reactor. The aim is thus to limit the temperature which thecatalyst can reach by very greatly diluting the gas stream and/or byadding inert heat-exchange compounds, such as steam or CO₂. Theregeneration then takes a great deal of time as a hot front movesthrough the catalyst bed corresponding to the combustion of the coke. Itis thus desirable to accelerate the reaction for regeneration bycombustion of the coke. This regeneration can be accelerated byincreasing the temperature and/or the oxygen partial pressure but thereis then a risk of encountering the disadvantages listed above. Thereactor of the invention makes it possible to space out the addition ofoxygen at several points of the reactor and consequently to carry out aregeneration while multiplying the hot fronts in the reactor. It is thusdesirable to inject the oxygen in multiple lines and preferably withlines spaced out every 5% to 33% of the length of the reactor andpreferably 10% to 20% of the length of the reactor.

The invention also makes it possible to carry out a process for thedehydration of lactic acid or 3-hydroxypropionic acid (and theircorresponding esters) to give acrylic acid.

Lactic acid has a boiling point in the vicinity of 217° C. and3-hydroxypropionic acid has a boiling point of 279° C. (calculatedvalue). The flammability limits for lactic acid in air are 3.1% (lowerlimit) and 18% (upper limit). The methyl ester of lactic acid has aboiling point of 145° C., for the flammability limits of 1.1% and 3.6%(which gives greater flexibility of use than for the acid). The methylester of 3-hydroxypropionic acid has a boiling point of 179° C. (180° C.as calculated value). The ethyl ester of lactic acid has a boiling pointof 154° C. and flammability limits of 1.6% and 10.6%. The ethyl ester of3-hydroxypropionic acid has a boiling point of 187.5° C.

For these reactions, use is made of a reactor configurationsubstantially identical to that for the dehydration of glycerol. Thedehydration conditions are a temperature of 220 to 400° C. andpreferably of 250 to 350° C. and a pressure of 0.5 to 5 bar.

The catalysts which may be suitable for these reactions are acidcatalysts, having in particular a Hammett acidity of less than +2. Thecatalysts can be chosen from natural or synthetic siliceous substancesor acidic zeolites; inorganic supports, such as oxides, covered withmono-, di-, tri- or polyacidic inorganic acids; oxides or mixed oxidesor heteropolyacids or heteropolyacid salts comprising in particular atleast one element chosen from the group consisting of W, Mo and V.Mention may particularly be made, among mixed oxides, of those based oniron and on phosphorus and of those based on cesium, phosphorus andtungsten.

Other catalysts which may also be suitable for these reactions areobtained from phosphates and/or sulfates of alkali metals, alkalineearth metals and rare earth metals, and their mixtures. This group thusincludes lanthanum phosphates and oxyphosphates, sodium phosphates,calcium phosphates, calcium sulfate, magnesium sulfate, and thecorresponding hydrogenphosphates, aluminum phosphate, boron phosphate.All the abovementioned active materials can be impregnated or coated onany type of support, such as: alumina, titanium oxide, zirconium oxideor silica, but also the corresponding mixed oxides, and silicon carbide.

The lactic acid or 3-hydroxypropionic acid partial pressure is generallyfrom 1% to 10% and preferably from 2% to 6%.

Still in the context of these reactions, the catalyst undergoesdeactivation, in particular by coking. This deactivation can be delayedby injecting oxygen in situ into the reaction compartments of thereactor, in the production phase. The conditions relating to theinjection of oxygen are the same as those described above in connectionwith the dehydration of glycerol.

Furthermore, in the regeneration phase, the injection of oxygen in situinto the reaction compartments of the reactor makes it possible toregenerate the catalyst in a safe and controlled manner. The conditionsrelating to the injection of oxygen are the same as those describedabove in connection with the dehydration of glycerol.

The invention also makes it possible to carry out a process for thedehydration of 2-hydroxyisobutyric acid or 3-hydroxyisobutyric acid togive methacrylic acid.

For this type of reaction, use is made of a reactor configurationsubstantially identical to that for the dehydration of glycerol. Thedehydration conditions are a temperature of 200 to 400° C., andpreferably of 250 to 350° C. and a pressure of 0.5 to 5 bar. Thecatalysts which may be suitable for this reaction are acid catalysts,having in particular a Hammett acidity of less than +2. The catalystscan be chosen from natural or synthetic siliceous substances or acidiczeolites; inorganic supports, such as oxides, covered with mono-, di-,tri- or polyacidic inorganic acids; oxides or mixed oxides orheteropolyacids or heteropolyacid salts comprising in particular atleast one element chosen from the group consisting of W, Mo and V.Mention may particularly be made, among mixed oxides, of those based oniron and on phosphorus and of those based on cesium, phosphorus andtungsten.

Catalysts which may also be suitable for this reaction are obtained fromphosphates and/or sulfates of alkali metals, alkaline earth metals andrare earth metals, and their mixtures. This group thus includeslanthanum phosphates and oxyphosphates, sodium phosphates, calciumphosphates, calcium sulfate, magnesium sulfate, and the correspondinghydrogenphosphates, aluminum phosphate, boron phosphate. All theabovementioned active materials can be impregnated or coated on any typeof support, such as: alumina, titanium oxide, zirconium oxide or silica,but also the corresponding mixed oxides, and silicon carbide.

The (2- or 3-)hydroxyisobutyric acid partial pressure is generally from1% to 10% and preferably from 2% to 6%.

Still in the context of these reactions, the catalyst undergoesdeactivation, in particular by coking. This deactivation can be delayedby injecting oxygen in situ into the reaction compartments of thereactor, in the production phase. The conditions relating to theinjection of oxygen are the same as those described above in connectionwith the dehydration of glycerol.

Furthermore, in the regeneration phase, the injection of oxygen in situinto the reaction compartments of the reactor makes it possible toregenerate the catalyst in a safe and controlled manner. The conditionsrelating to the injection of oxygen are the same as those describedabove in connection with the dehydration of glycerol.

The invention also makes it possible to carry out selective oxidations,such as the oxidation of methanol to give formaldehyde ordimethoxymethane; the oxidation of ethanol to give acetaldehyde ordiethoxyethane; the oxidation of ortho-xylene or naphthalene to givephthalic anhydride; or the oxidation of benzene, butene, butanol orbutane to give maleic anhydride.

In these oxidation reactions, the shared problem is that of injecting,at the reactor inlet, a sufficient amount of oxygen (or other oxidizingagent) to ensure complete conversion or at least the highest possibleconversion of the hydrocarbon reactant while making sure to limit therisks of runaway of the reactor and the risks of explosion. The solutionselected comes down to limiting the productivity of the reactors bylimiting the partial pressure of the hydrocarbon compound. The inventionmakes it possible to use lower O₂/hydrocarbon reactant ratios at thereactor inlet, the remainder of the oxygen necessary for the reactionbeing introduced by the injection devices.

In the case of the reactions for the oxidation of methanol to giveformaldehyde or dimethoxymethane and for the oxidation of ethanol togive acetaldehyde or diethoxyethane, the catalysts which may be suitableare mixed oxides, such as iron molybdenum oxides or molybdenum oxidescomprising metals chosen from bismuth, vanadium, tungsten, copper,nickel or cobalt. The operating conditions are a temperature of between200 and 350° C., preferably between 250 and 300° C., and a pressure ofbetween 1 and 5 bar. The alcohol partial pressure can vary within a widerange from 3% to 50% and preferably from 5% to 40%, according to thetype of product desired. In the case where the aldehydes are the desiredproducts, the alcohol partial pressure is between 3% and 10% andpreferably between 5% and 9%. In the case where the acetals are thedesired products, the alcohol partial pressure is between 10% and 50%and preferably between 20% and 40%.

In the case of the reactions for the oxidation of ortho-xylene andnaphthalene to give phthalic anhydride, the catalysts selectedpreferably comprise vanadium and preferably supported vanadium oxide.The operating conditions are a pressure of 1 to 5 bar and reactiontemperatures of 280 to 450° C.

In the case of the reactions for the oxidation of butane, butenes,butanol and benzene to give maleic anhydride, the catalysts which aresuitable comprise vanadium, in the form of supported vanadium oxide orin the form of supported mixed vanadium/phosphorus oxide. The reactiontemperatures are from 350 to 500° C. and the pressures are from 1 to 5bar.

In the case of the reactions for the oxidation of propylene to giveacrolein or of isobutene or tert-butanol to give methacrolein, thecatalysts which are suitable consist predominantly of molybdenum andcomprise elements chosen from (but not exclusively) the followingelements: nickel, iron, cobalt, tungsten, potassium, bismuth, antimonyor chromium. The reaction temperatures are between 320 and 450° C. Thetotal pressures are between 1 and 5 bar. The hydrocarbon compoundpartial pressures are between 5% and 15% and the O₂/hydrocarbon compoundratio at the reactor inlet is between 0.5 and 4, preferably between 0.8and 2, more preferably still between 1 and 1.8 and more preferablybetween 1.2 and 1.6.

In the case of the reactions for the oxidation of acrolein to giveacrylic acid and of methacrolein to give methacrylic acid, the catalystswhich are suitable consist predominantly of molybdenum and compriseelements chosen from the following elements (but not exclusively):vanadium, tungsten, copper, antimony, niobium, strontium, phosphorus oriron. The operating temperatures are between 250 and 350° C., for atotal pressure of 1 to 5 bar. The aldehyde partial pressure is between5% and 15% and the O₂/aldehyde ratio at the reactor inlet is between 0.3and 1.2 and preferably between 0.5 and 1.

Other oxidation reactions which can be carried out according to theinvention are:

-   -   The production of acrylic acid from propylene and oxygen, the        coproducts being acrolein, acetic acid, maleic acid, propionic        acid, acetaldehyde and acetone, for example at a temperature of        300 to 400° C. and at a pressure of 1 to 3 bar.    -   The production of ethylene oxide from ethylene and oxygen, the        coproducts being acetaldehyde and formaldehyde, for example at a        temperature of 230 to 290° C. and at a pressure of 10 to 30 bar.    -   The production of 1,2-dichloroethane from ethylene, hydrochloric        acid and oxygen, the coproducts being carbon monoxide, chloral        and various chlorinated compounds, for example at a temperature        of 220 to 300° C. and at a pressure of 2 to 6 bar.    -   The production of terephthalic acid from p-xylene and oxygen,        the coproducts being maleic anhydride, o-toluic acid and benzoic        acid, for example at a temperature of 175 to 230° C. and at a        pressure of 15 to 30 bar.

The reactor according to the invention may also be suitable forammoxidation reactions involving ammonia/oxygen/inert gas/hydrocarboncompound mixtures. The hydrocarbon compounds which can be used comprisepropylene, isobutene, acrolein, methacrolein but also aromaticcompounds. The ammoxidation reactions are carried out at a temperaturefrom 50 to 100° C. higher than the corresponding oxidation temperatures.The reactor according to the invention makes it possible to inject oneor other reactant by the injection devices. Optionally, the injectedreactants can be alternated along the length of the reactor. Preferably,the oxygen (or the air/enriched air) is injected by the injectiondevices. Nevertheless, in the case of the ammoxidation reactions of analdehyde, such as acrolein, the multi-stage injection of the ammonia bythe injection devices makes it possible to limit side reactions whichtend to form deposits at the reactor inlet.

By way of example, acrylonitrile (while coproducing acetonitrile,hydrocyanic acid and carbon monoxide) can be produced from propyleneand/or propane, oxygen and ammonia, for example at a temperature of 400to 500° C. and at a pressure of 1 to 4 bar.

The invention also makes it possible to carry out a fluorinationprocess, that is to say a process for the preparation of a fluorinatedcompound from a chlorinated compound. Preferably, the reaction iscarried out by reacting the chlorinated compound with hydrogen fluoride(HF).

The chlorinated compound can be any molecule having at least onechlorine atom and the fluorinated compound can be any molecule having atleast one fluorine atom.

Preferably, the chlorinated compound is a linear or branched (preferablylinear) C₂ or C₃ or C₄ or C₅ alkane or alkene comprising one or moresubstituents chosen from F, Cl, I and Br (preferably from F and Cl), atleast one of the substituents being Cl.

Preferably, the fluorinated compound is a linear or branched (preferablylinear) C₂ or C₃ or C₄ or C₅ alkane or alkene comprising one or moresubstituents chosen from F, Cl, I and Br (preferably from F and Cl), atleast one of the substituents being F.

More particularly preferably, the chlorinated compound is a C₃ alkane oralkene comprising one or more substituents chosen from F, Cl, I and Br(preferably from F and Cl), at least one of the substituents being Cl,and the fluorinated compound is a C₃ alkene comprising one or moresubstituents chosen from F, Cl, I and Br (preferably from F and Cl), atleast one of the substituents being F.

Alternatively, the chlorinated compound can be a C₄ alkane or alkenecomprising one or more substituents chosen from F, Cl, I and Br(preferably from F and Cl), at least one of the substituents being Cl,and the fluorinated compound is a C₄ alkene comprising one or moresubstituents chosen from F, Cl, I and Br (preferably from F and Cl), atleast one of the substituents being F.

According to one embodiment, the fluorinated compound is ahydrofluoroolefin (and thus does not comprise a Cl substituent).

Preferably, during the reaction, at least one Cl substituent of thechlorinated compound is replaced by an F substituent.

The conversion of the chlorinated compound to the fluorinated compoundcomprises the direct conversion (in just one stage or according to justone combination of operating conditions) and the indirect conversion (intwo or more than two stages or by using more than one combination ofoperating conditions).

The fluorination reactions more particularly preferred are thereactions:

-   -   of 2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 1,1,1,2,3-pentachloropropane (HCC-240db) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 1,1,2,2,3-pentachloropropane (HCC-240aa) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 1,1,2,3-tetrachloro-1-propene (HCO-1230xa) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 2,3,3,3-tetrachloro-1-propene (HCO-1230xf) to give        2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);    -   of 1,1,1,2,3-pentachloropropane (HCC-240db) to give        2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);    -   of 1,1,2,2,3-pentachloropropane (HCC-240aa) to give        2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);    -   of 2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) to give        2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);    -   of 1,1,2,3-tetrachloro-1-propene (HCO-1230xa) to give        2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);    -   of 2,3,3,3-tetrachloro-1-propene (HCO-1230xf) to give        2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf).

The fluorination reaction can be carried out with an HF molar ratiotypically of 3:1 to 150:1, with a contact time of 6 to 100 s and at apressure from atmospheric pressure to 20 bar. The temperature of thereaction can be from 200 to 450° C.

A specific example of the process which makes it possible to prepareHFO-1234yf from HFCO-1233xf occurs in the document WO 2010/123154. Thisprocess can be carried out with the reactor according to the invention.

The catalyst used for the above fluorination reactions may or may not besupported.

It can, for example, be a metal catalyst, that is to say of theelemental metal, metal oxide, metal halide and/or metal salt type, inparticular a transition metal oxide or a halide or oxyhalide of such ametal.

It can in particular be antimony halide, tin halide, thallium halide,titanium halide, iron halide and a combination of these. Metal chloridesand fluorides are preferred, for example SbCl₅, SbCl₃, SbF₅, SnCl₄,TiCl₄, FeCl₃ and the combinations of these.

Other appropriate catalysts are those based on chromium, such aschromium oxyfluoride, chromium oxides, such as Cr₂O₃ (optionallysubjected to fluorination treatments), chromium fluorides and thecombinations of these.

Other possible catalysts are those based on aluminum (for example AlF₃,Al₂O₃ and aluminum oxyfluoride).

The catalyst can be chosen from fluorinated alumina, fluorinatedtitanium dioxide, fluorinated stainless steel, active charcoal andgraphite.

It can be a mixture of chromium and magnesium (in the elemental, saline,oxide or halide form) or a mixture of chromium and another metal (in theelemental, saline, oxide or halide form).

It can also be a catalyst comprising a metal on a support.

The metal can be chosen from Groups 3, 4, 5, 6, 7, 8, 9 and 13 of thePeriodic Table and can in particular be Al, Cr, Mn, Co, Ni, Zn, Ti, V,Ru, Rh, Pd, Os, Ir, Pt, Zr, Mo, Re, Sc, Y, La, Hf, Cu, Ag, Au, Ge, Sn,Pb or Mg, in particular Al, Cr, Mn, Ni or Co. It can be a lanthanide(metals 58 to 71 of the Periodic Table). The metal of the catalyst canbe converted into metal derivatives during its activation or itsregeneration, for example into oxide, halide (fluoride, bromide,chloride), oxyhalide or pseudohalide (cyanide, cyanate, thiocyanate).

The support can be chosen from aluminum, aluminum halides and aluminumoxyhalides, alumina, activated alumina, fluorinated alumina, aluminumfluoride, active charcoal (fluorinated or non fluorinated) and graphite(optionally fluorinated).

The catalyst can be prepared, for example, by immersion of the supportin a solution of soluble compound (for example, nitrate or chloride) ofthe metal, or alternatively the solution can be sprayed onto thesupport. The support can be dried and brought into contact with ahalogenating agent in the vapor form (for example, hydrogen fluoride,hydrochloric acid, chlorofluorohydrocarbon, or also SiF₄, CCl₃F, CCl₂F,CHF₃ or CCl₂FCClF₂) with heating in order to partially or completelyhalogenate the support or the metal.

Examples of supported catalysts are FeCl₃ supported on carbon, aluminasupported on carbon, aluminum fluoride supported on carbon, fluorinatedalumina supported on carbon, magnesium fluoride supported on aluminumfluoride, more generally metals (elemental metals, metal oxides, metalhalides and/or metal salts) supported on aluminum fluoride, metalssupported on alumina, metals supported on carbon, or the mixtures ofmetals.

Other examples of supported catalysts are: a magnesium halide or a zinchalide supported on Cr₂O₃, a chromium(III) halide supported on carbon, amixture of chromium and magnesium (in the elemental, oxide, halide orsaline form) supported on graphite, a mixture of chromium and anothermetal (in the elemental, saline, oxide or halide form) supported ongraphite or alumina or an aluminum halide, such as aluminum fluoride.

The total metal content of the supported catalyst is preferably from0.1% to 20% by weight, for example from 0.1% to 10% by weight (withrespect to the total weight of the catalyst).

A preferred embodiment uses a specific catalyst which is a supportedmixed catalyst comprising both chromium and nickel. The Cr:Ni molarratio (with respect to the metal elements) is generally from 0.5 to 5,for example from 0.7 to 2 and in particular in the vicinity of 1. Thecatalyst can comprise from 0.5% to 20% of chromium and from 0.5% to 20%of nickel by weight, preferably from 2% to 10% of each metal. Referencecan be made, in this regard, to the document WO 2009/118628 and inparticular to the description of the catalyst from p.4, 1.30, to p.7,1.16.

An advantageous catalyst is a chromium-based catalyst comprising achromium compound of the crystalline alpha-chromium oxide type, in whichfrom 0.05% to 6% of the atoms approximately of the alpha-chromium oxidelattice are replaced with trivalent cobalt atoms (optionally treatedwith a fluorinating agent). Reference is made to the document US2005/0228202 on this subject.

The catalyst can be subjected to a fluorination. As example offluorination, it is possible to prepare a fluorinated alumina bybringing an alumina into contact with hydrogen fluoride with heating orby spraying an aqueous hydrogen fluoride solution at ambient temperatureor by immersing an alumina in solution, and by then drying. Thefluorination of the catalyst may or may not be carried out in thereactor according to the invention. The temperature during thefluorination is generally from 200 to 450° C.

The catalyst can optionally comprise a low content of one or morecocatalysts, such as Co, Zn, Mn, Mg, V, Mo, Te, Nb, Sb, Ta, P and Nisalts. A preferred cocatalyst is nickel. Another preferred cocatalyst ismagnesium.

For example, an unsupported chromium-based catalyst can optionallycomprise a low content of one or more cocatalysts chosen from cobalt,nickel, zinc or manganese and be prepared by processes known per se,such as impregnation, mixing of powders and others.

The amount of cocatalyst, when it is present, can vary from 1% to 10% byweight, preferably from 1% to 5% by weight. The cocatalyst can be addedto the catalyst by processes known per se, such as adsorption from anaqueous or organic solution, followed by the evaporation of the solvent.A preferred catalyst is pure chromium oxide with nickel or zinc ascocatalyst. Alternatively, the cocatalyst can be physically mixed withthe catalyst by grinding, in order to produce a fine mixture.

Another preferred catalyst is a mixed chromium/nickel catalyst supportedon fluorinated alumina. The document U.S. Pat. No. 5,731,481 describes aprocess for the preparation of this other catalyst.

Before activation, the catalyst is subjected to a stage of drying,preferably with a drying gas, such as nitrogen. The drying stage can becarried out at a pressure ranging from atmospheric pressure to 20 bar.The temperature of the catalyst during the drying stage can range from20° C. to 400° C., preferably from 100° C. to 200° C.

The activation of the catalyst can preferably be carried out with HF ora fluoro- or hydrofluoroalkane and/or an oxidizing agent (preferablyoxygen or chlorine). The regeneration of the catalyst can be carried outwith an oxidizing agent (preferably oxygen or chlorine) and optionallyHF, in one or more stages.

In order to extend the duration of deactivation of the catalyst, it ispossible to add an oxidizing agent (preferably oxygen or chlorine)during the production phase, for example in a proportion of 0.05 mol %to 15 mol %, with respect to the mixture of oxidizing agent andchlorinated compound.

The temperature during the regeneration stage can be from 250 to 500° C.approximately and the pressure from atmospheric pressure toapproximately 20 bar. When HF is used in combination with oxygen, theproportion of oxygen can vary from 2 mol % to 98 mol %, with respect tothe HF/oxygen mixture.

The invention makes it possible in particular to carry out the injectionof oxygen (or of chlorine) in situ into the reactor in the productionphase and/or in the regeneration phase, and also optionally for theinitial activation of the catalyst.

1. A chemical reactor comprising: a plurality of heat-exchange platesdefining, between them, reaction compartments, in which reactor eachheat-exchange plate comprises two walls defining, between them, at leastone heat-exchange space, the respective walls being fixed to one anotherby joining regions, and the reactor also comprises at least one devicefor injection of substance into the reaction compartments, saidsubstance-injecting device passing through the heat-exchange plates inrespective joining regions of the plates.
 2. The chemical reactor asclaimed in claim 1, in which the substance-injecting device is a devicefor the injection of gas.
 3. The chemical reactor as claimed in claim 1,in which the substance-injecting device is a pipe exhibiting a pluralityof injection orifices.
 4. The chemical reactor as claimed in claim 1, inwhich the joining regions are positioned on the heat-exchange plates inthe form of strips or in the form of points.
 5. The chemical reactor asclaimed in claim 1, comprising: a plurality of substance-injectingdevices.
 6. The chemical reactor as claimed in claim 1, in which theheat-exchange plates are positioned in a chamber in a radial manner orin a manner parallel to one another.
 7. A chemical reaction processcomprising: the admission of reactants at the inlet of a reactioncompartment defined between two heat-exchange plates, the withdrawal ofreaction products at the outlet of the reaction compartment, and theinjection of a substance into the reaction compartment, in which processeach heat-exchange plate comprises two walls defining, between them, atleast one heat-exchange space, the respective walls being fixed to oneanother by joining regions, and the injection of substance being carriedout by means of at least one substance-injecting device which passesthrough the heat-exchange plates in respective joining regions of theplates.
 8. The process as claimed in claim 7, in which the reaction isof the heterogeneous catalytic type and a catalyst is positioned in thereaction compartments.
 9. The process as claimed in claim 7, alternatelycomprising: phases of production and phases of regeneration of thecatalyst, the injection of substance being carried out during thereaction phases and/or during the regeneration phases.
 10. The processas claimed in claim 7, in which the substance is a reactant or acatalytic compound or a compound capable of regenerating a catalyst. 11.The process as claimed in claim 7, in which the substance is anoxygen-comprising gas.
 12. The process as claimed in claim 7, in whichthe substance is injected at several points of the route of thereactants in the reaction compartment.
 13. The process as claimed inclaim 7, carried out in a chemical reactor.
 14. The process as claimedin claim 7, which is: a process for the dehydration of glycerol to giveacrolein; or a process for the dehydration of lactic acid to giveacrylic acid; or a process for the dehydration of 3-hydroxypropionicacid to give acrylic acid; or a process for the dehydration of3-hydroxyisobutyric acid to give methacrylic acid; or a process for thedehydration of 2-hydroxyisobutyric acid to give methacrylic acid; or aprocess for the conversion of a chlorinated compound into a fluorinatedcompound; or a selective oxidation process selected from the following:the oxidation of methanol to give formaldehyde or dimethoxymethane; theoxidation of ethanol to give acetaldehyde or diethoxyethane; theoxidation of ortho-xylene or naphthalene to give phthalic anhydride; theoxidation of benzene, butene, butanol or butane to give maleicanhydride; the oxidation of propylene to give acrolein; or the oxidationof isobutene or tert-butanol to give methacrolein.
 15. The chemicalreactor as claimed in claim 1, in which the substance-injecting deviceis a device for the injection of oxygen-comprising gas.
 16. The chemicalreactor as claimed in claim 1, in which the joining regions arepositioned on the heat-exchange plates in the form of parallel strips.17. The chemical reactor as claimed in claim 1, comprising: a pluralityof substance-injecting devices parallel to one another and connected toa substance-distributing system.
 18. The chemical reactor as claimed inclaim 1, in which the heat-exchange plates are positioned in a chamberin a radial manner or in a manner parallel to one another and aregrouped into modules.
 19. The process as claimed in claim 7, in whichthe reaction is of the heterogeneous catalytic type and a catalyst ispositioned in the reaction compartments in the form of solid particles.